Are "natural" sunscreens truly free of chemicals?

Sunscreens with physical blockers—like zinc oxide—are generally thought of as natural because they come from minerals; those made with avobenzone are officially classified as "chemical." The truth: Zinc oxide and titanium dioxide are put through a chemical process before they end up in the bottle, so they aren't totally natural, either.

Three reasons you could be sun-vulnerable

1. You're on oral or topical medications. Even if you wear sunscreen, certain antibiotics for treating acne and urinary tract infections, as well as isotretinoin (aka Accutane), some blood pressure meds and sulfur creams can all leave you fried. That's because "some drugs break into tiny particles when they penetrate skin or enter the bloodstream; these can react with UV rays and cause a burn," Dr. Marmur says. Vacationing in the sun? Ask your doctor if you could temporarily stop taking your Rx about two weeks before you go, to minimize your chances of getting scorched.

Three reasons you could be sun-vulnerable

2. You're on hormones or you're pregnant (or trying to be).The Pill and some hormone regimens (e.g., those for infertility treatments) can cause melasma, a type of sun-induced pigmentation.

3. You have a health condition. Certain autoimmune diseases (such as lupus) can increase vulnerability to sun rashes. Some folks also have a sun allergy, aka polymorphous light eruption, in which a rash arises after even intermittent UV exposure. Stay in the shade!